I have a 2011 Chev and had the DPF delete done in Jan. Truck runs great... Recently though the Stabilitrak would give me issues... The left front brake would pulse and then I would get a message to "Service Stabilitrak", then the truck would drive fine until you restarted it. Not always though, seemed selective.
Became more persistant until tonight...
I drove the family to DQ to get ice cream at the drive thru. turned off the motor to talk to the girl, made the order and fired up the truck and drove to the window. While we were waiting I was dusting the dash, cleaning a little (I think its unrelated but thought I'd mention it anyway), put the truck in Drive to pull away from the window and no gear position indication, didn't want to move. change gear to manual and nothing, can't even change gears manually.
Park assist won't work, message shows up to "service Stabilitrak" still, traction control off, hard shifting into reverse or drive. Drive home and put it in the driveway. Check fuses and trans fluid... all good. Take for another drive alone and it seems like it's stuck in 2nd or even 3rd gear, won't kick down, very sluggish...

I don't have a code reader and I had planned to take my quad to a rally tomorrow but that seems to be in question now.
Hoping for an easy fix but I have my doubts...